Calenders are mechanisms that include a series of pairs of rolls through which a substance that is malleable can be run in order to smooth out the material and form a skim or sheet of uniform thickness. In the tire industry, calenders are used to process an elastomeric or rubber mix that is usually extruded and then sent through the calender to create a sheet of rubber or elastomer mix. Between each pair of rolls is a gap or nip through which the material is run as the rolls are rotated. Depending on a host of processing variables, the sheet will assume some thickness that is proportional to the width of the nip. Often, the material is fed through three sets of rolls and nips in order to create a homogenous and smooth sheet that also has a desired thickness, as is the case for an inverted “L” configured calender as will be described shortly. This sheet is then used to create some portion of the tire, such as the tread or other semi-finished goods used to manufacture and assemble the tire such as belts and carcass plies, etc.
An illustration of such a typical calendering system 10 is shown in FIGS. 1 and 2, which has three pairs of rolls (labeled as rolls 12, 14, 16, and 18) with a nip between pairs as well as a fifth roll 20, sometimes referred to as a take-off roll, that takes the sheet as it comes off the fourth roll 18. The purpose of this roll 20 is to provide tension to remove the sheet 22 as it exits the calender. The calender rolls that are part of a pair rotate in opposite directions or in the same linear direction/surface direction in the nip area 24 so that material that is fed into the entrance 26 of the nip is forced through the nip into the exit area 28 of the nip. For the first pair of rolls, the entrance of the nip is located above the rolls so that material is naturally fed into the nip via gravity upon startup or just before. Usually, a bank 30 of kneaded material (sometimes referred to as a bourelet by the inventor(s)) collects above the nip of the first pair of rolls so that enough material is present to form an uninterrupted sheet of material that can pass through the calendering system. This bank is created by oversupplying slightly the amount of material needed to create the sheet of material from a source of the material such as an extruder. In time, material is forced downward into the nip by the rotation of the rolls.
After exiting the first nip area 24a, the material then winds in a counterclockwise direction around the second roll 14 until it is reaches the third roll 16 where it goes through a second nip area 24b. Once it exits, the material then winds in a clockwise direction around the third roll 16 and then encounters the fourth roll 18 where it goes through the third nip area 24c. At this point, the sheet then attaches to the fourth roll 18 where it is rotates in a counterclockwise direction once more around the bottom and part of the back of the fourth roll 18 and on top of the fifth roll 20, which is rotated in the clockwise direction and which is biased upwards to place the sheet in tension before it proceeds to a production center where some tire component is made using the sheet of material. This desired path is shown by the solid outline of material whereas an unintended circulation of material is represented by the dashed arrows as will be described in further detail later.
All the rolls or pairs of rolls can be commonly driven by a single motor using gears, chains, or belts. In such a case, the speed of all the rolls or of the rolls of a pair can be the same or can be different utilizing some sort of transmission system such as a variable speed ratio reducer between the rolls and the motor. Alternatively, all the rolls can be independently driven using a separate motor for each roll. In that case, electronic controls are sometimes furnished that allow tight and independent control of the speed of each roll by way of suitable programming by the operator or some other control algorithm executed by a computer. For example of rolls that are independently driven or that can operate at different adjustable speeds. See, e.g., U.S. Pat. Nos. 2,333,629; 4,444,361; and G.B. Pat. Nos. 856,454; 620,340.
An example of a production center that can be fed by a calender system is depicted by FIG. 3, which is disclosed in U.S. Patent Application Publication No. 20110036485, which is commonly owned by the assignee of the present invention and whose content is incorporated by reference for all purposes in its entirety. Portions of that application are reproduced herein as follows to describe how the process works and how it can be used in conjunction with the present invention. It should be noted that this is given by way of an example of a production center and that the present invention is equally applicable to any manufacture of a tire component that requires a calendering system of any sort including those that only have a single pair of rolls.
A system 110 for generating a multi-layered tire component in accordance with the methods described in the '485 application is generally shown in FIG. 3. System 110 generally operates to form a multi-layered tire component by winding strips 141 about a building surface. Because a tire component is a wound product, it generally forms a complete circle (i.e., a ring). The component is also referred to herein as a band. Also, system 110 generates a sheet 121 from which the strips 141 are formed, and, in particular embodiments, the sheet 121 remains continuous as it travels along a closed-loop path to and from a sheet generator 120. Accordingly, system 110 automatically returns any unused sheet material for reuse by generator 120. System 110 generally forms elastomeric tire components, such as, for example, tread, sub-tread, and cushion gum. It can also create a multi-layered band that is a profiled tire tread band.
In this embodiment, system 110 comprises a sheet generator 120, a cutting assembly 140, a strip applicator assembly 160, a recovery assembly 170, and a programmable logic control (not shown). System 110 may also include a roll assembly 130 for directing a sheet 121 from generator 120 to cutting assembly 140. Sheet generator 120 generally transforms input material 112 into a sheet 121, which is ultimately cut into strips 141 by cutting assembly 140.
With continued reference to FIG. 3, input material 112 is received through inlet 122, and may comprise new material 112a and/or previously used material 112b supplied by recovery assembly 170. After receiving input material 112, generator 120 forms the input material by any known means such as by a calendering system shown in FIGS. 1 and 2 and described above into sheet 121, where sheet 121 is formed to any desired width and thickness. Sheet 121 is expelled from generator 120 by way of outlet 123.
In one embodiment, as shown in FIG. 3, generator 120 comprises an extruder. Extruders generally push input material 112 through a die or head, such as by way of a screw. Any extruder known to one of ordinary skill in the art may be used by system 110. Generator 120 may also comprise a calender in lieu of, or in addition to, an extruder, which may comprise a pair of rolls positioned in close proximity to each other to form a gap or nip, through which input material 112 passes to from a sheet 121 (as described above). The resulting sheet 121 includes a width associated with the width of the calender nip. While an extruder and calender are capable of operating at similarly high speeds, a calender may not be as readily adjustable to changes in speed. This may affect the start-up time of system 110, as well as the responsiveness of system 110 to restart after a temporary delay.
As shown in FIG. 3, a roll assembly 130 may be located between sheet generator 120 and cutting assembly 140. Roll assembly 130 generally comprises one or more rolls 132 arranged to form a translation path of sheet 121. The take up roll described above in FIGS. 1 and 2 may be considered as such a roll. The particular translation path directs sheet 121 to cutting assembly 140, and may be used to tense sheet 121 as desired. The location of rolls 132 may be adjusted to impart more or less tension on sheet 121, which may also provide a means for adjusting the cross-sectional dimensions of sheet 121. One or more rolls 132 may be driven or powered, such as, for example, by a motor, to assist in the translation of sheet 121, and/or adjustment of tension in sheet 121. In addition, biasing means such as springs, pneumatic or hydraulic cylinders, etc. may force the roll against the sheet to provide tension. Sheet 121 may also be tensed by creating a speed differential between drum 125 and/or cutting drum 152, by increasing or decreasing the rotational speed of either drum.
Cutting assembly 140 generally forms strips 141 from sheet 121 for subsequent assembly of the tire band. More specifically, cutting assembly 140 utilizes a plurality of cutting members 142 to cut strips 141, wherein each cutting member 142 includes a cutting edge 143. Cutting members 142 generally are spaced along a length of sheet 121, and along a circumference of cutting surface and/or cutting drum 152. In the embodiment shown in the FIGURES, cutting members 142 are rotating knives. Rotating knives, in the embodiment shown, operate similarly to idler wheels, and freely rotate at the direction of the translating sheet 121. Still, rotating knives 142 may be driven by a motor or any other known driving means. Also, other means for cutting sheet 121 known to one of ordinary skill in the art may be used in lieu of rotating knives, including other non-rotating knives, blades, or edges.
With general reference to FIG. 3, system 110 also includes an applicator assembly 160 for applying one or more continuous strips 141 to a building surface to form a band. The one or more strips 141 are wound about the building surface to form the multi-layered band. Applicator assembly 160 includes an applicator drum 162 that transfers one or more strips 141 there from to building assembly 180. To provide adhesion between applicator drum 162 and strips 141, which promotes the separation of strips 141 from sheet 121, applicator drum 162 may be heated or cooled. In particular embodiments, applicator drum 162 is maintained at a temperature at least 10 degrees Celsius higher than the temperature of sheet 121 and/or any strips 141. In other embodiments, applicator drum 162 is maintained at approximately 70 degrees Celsius. The surface of applicator drum 162 may comprise a smooth surface, which may be a chromed or hot chromed surface, so to provide a smooth, capillary-like surface that may promote molecular bonding and/or may operate like a vacuum to facilitate retention of strips 141 thereon. Improved adhesion may also be provided by providing a rough surface, the rough surface providing increased surface area for improved contact area, and therefore, increased adhesion. Applicator drum 162 may also operate as the cutting drum 152. Further, the temperature controls and conditions, as well as the surface conditions and treatments discussed with regard to applicator drum 162 above may also be applied to cutting drum 152 to improve adhesion between drum 152 and sheet 121. Using this system, tread features can be built onto a green or uncured tire layer by layer.
As just described regarding the applicator or cutting drum, the adhesion of rubber strips to a round and rotating surface is apt to occur. Accordingly, when multiple rotating surfaces are present near the exit of the nip of calender rolls, e.g. their respective circumferential surfaces that are rotating away from nip exit, a sheet of elastomeric mix can bond with either of these surfaces, or partially to both at the same time. This can be a problem during the operation of the calender, but especially during the initialization or start-up of the calender as an initial sheet needs to be directed, often by an operator, to follow the proper path until the calender has been successfully “threaded” and is ready to supply a sheet of material to the desired production center. This requires shut-down of the equipment for safety reasons, which can be costly.
Looking back at FIG. 2, the desired path is denoted by a solid outline of material and an unwanted path by dashed arrows. As can be seen, the first unwanted path can occur when the sheet sticks to the first roll 12 where it rotates clockwise away from the exit 28a of the first nip 24a. This can lead it back to the top bank 30a of kneaded material, creating an undesirable feedback loop where excessive material will spill off the axial ends of the roll and down the sides of the calendering apparatus, potentially causing damage to the apparatus or other equipment by gumming up the equipment and stopping production. A similar situation can occur when the sheet exits the second nip 24b as it can continue to run clockwise on the second roll 14 and into the top bank of material 30a. After the third nip 24c, the material can recycle itself back to the second nip 24b, creating unwanted growth of a second bank 30b of material. Finally, after the sheet comes back around the bottom of the fourth roll 18, it can continue to stick to this roll and create a third bank 30c of material near the entrance 26c of the third nip 24c. 
Any of these banks of material can become too large and cause the equipment problems. Even after initially threading the calender, all three banks can occur due to some small residue sticking to the rolls and collecting near the entrance to the nips over time, thereby causing some small amount of recycling. Also, there is a desired amount of slight oversupply from each nip to the next that helps to ensure enough material is present for the step reduction in skim thickness at each nip which creates a full width sheet that is smooth, homogenous and that has the correct thickness. So, it is desirable to control the size of the banks of material but not to eliminate them altogether.
The reason elastomeric mixes are tacky will now be explained. Suitable compositions for making a sheet for use in tire components such as treads include those rubber compositions having a glass transition temperature within a defined range, said rubber compositions being based upon a diene elastomer, a plasticizing system and a cross-linking system. The diene elastomers or rubbers that are useful for such rubber compositions are understood to be those elastomers resulting at least in part, i.e., a homopolymer or a copolymer, from diene monomers, i.e., monomers having two double carbon-carbon bonds, whether conjugated or not.
In summary, typical diene elastomers include highly unsaturated diene elastomers such as polybutadienes (BR), polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers include butadiene/styrene copolymers (SBR), isoprene/butadiene copolymers (BIR), isoprene/styrene copolymers (SIR) and isoprene/butadiene/styrene copolymers (SBIR). Suitable elastomers may also include any of these elastomers being functionalized elastomers.
In addition, the elastomeric composition disclosed herein may further include a reinforcing filler. Reinforcing fillers are added to, inter alia, improve the tensile strength and wear resistance of the material. Any suitable reinforcing filler may be suitable for use in compositions disclosed herein including, for example, carbon blacks and/or inorganic reinforcing fillers such as silica, with which a coupling agent is typically associated. Inorganic reinforcing fillers may take many useful forms including, for example, as powder, microbeads, granules, balls and/or any other suitable form as well as mixtures thereof. Examples of suitable inorganic reinforcing fillers include mineral fillers of the siliceous type, such as silica (SiO2), of the aluminous type, such as alumina (AlO3) or combinations thereof.
For coupling the inorganic reinforcing filler to the diene elastomer, a coupling agent that is at least bifunctional provides a sufficient chemical and/or physical connection between the inorganic reinforcement filler and the diene elastomer. Examples of such coupling agents include bifunctional organosilanes or polyorganosiloxanes. Such coupling agents and their use are well known in the art. The coupling agent may optionally be grafted beforehand onto the diene elastomer or onto the inorganic reinforcing filler as is known. Otherwise it may be mixed into the rubber composition in its free or non-grafted state.
In addition to the diene elastomer and reinforcing filler, particular embodiments of the rubber composition disclosed herein may further include a plasticizing system. The plasticizing system may provide both an improvement to the processability of the rubber mix and/or a means for adjusting the rubber composition's glass transition temperature and/or rigidity. Suitable plasticizing systems may include a processing oil, plasticizing resin or combinations thereof. Other plasticizing systems are known. Table I below provides an example of rubber mixes that may be used with the present invention and, more particularly, indicates the percentage of resin and plasticizer that may be present and the type of resin. Other mixes may be used as well. Of resin types, limonene resin is one of the stickiest and was used in tests (discussed below) to demonstrate the efficacy of the invention.
TABLE I% Total PlasticizerMix% Resin(include oil and resin)Resin Type18.721.8Limonene215.620.4Limonene37.07.0Formophenolic(i.e. tackifier resin)
Also, the rubber compositions disclosed herein may have, or be cured with, any suitable curing system including a peroxide curing system or a sulfur curing system, many of which are known in the art. Other additives can be added to the rubber compositions disclosed herein as known in the art. Such additives may include, for example, some or all of the following: antidegradants, antioxidants, fatty acids, pigments, waxes, stearic acid and zinc oxide.
These constituents, notably the polymers used in the elastomeric mix, make the sheet sticky or have tack. Increasing the amount or type of certain ingredients such as pigments, fillers, additives, and plasticizers can increase tack. Also, some polymers have inherently more tack than others. Consequently, different mixes have more tack than others and can therefore be more prone to the problems just described.
As can be imagined, a number of methods have been devised to control or eliminate unwanted sticking of the sheet of material to calender rolls. Some methods have been already described above and include providing a temperature or surface finish differential between the two rolls that define a nip so that the sheet of material is prone to stick to one versus the other. Also, surface treatments that decrease adhesion to the roll to which adherence is undesirable after the sheet exits the nip can be applied to that roll. Such treatments include TEFLON, alkanolamines, alkylene glycols, and polyalkylene glycols (see U.S. Pat. No. 3,841,899). In Japanese Patent Application Publication No. JP9201838A, there is disclosed a method of continually applying a release agent on a roll using a soft roll onto which the agent is sprayed that rubs against the roll for solving sticking problems associated with that roll. Finally, the use of scraper blades is often used to prevent the unwanted recycling of material that can contribute to bank growth over time (See Jap. Pat. Application Publication No. 08-197558 A and U.S. Pat. No. 4,221,022 for examples). Also, the use of scraper blades to prevent the improper threading of a sheet processed by a calender processing elastomeric mixes, preventing it from recycling to the entrance of the nip thereby aiding in the start-up of a calendering process is also known (see col. 3, lines 5-10 of U.S. Pat. No. 4,871,409).
However, all these methods have drawbacks. Concerning maintaining the temperature of the rolls, it is necessary to maintain consistency the entire time the calendering apparatus is running, which could be difficult depending on ambient conditions. Also, this method could delay start-up until the rolls reach the desired temperature. Surface treatments that are applied to rolls such as disclosed in U.S. Pat. No. 3,841,800 can wear off over time which adds cost to reapply the treatment and possibly some downtime for the equipment. Continuously applying a release agent can be both expensive and messy, and may cause the agent to seep into the material causing a degradation of the properties of the sheet of material. Finally, scraper blades do not allow for the automatic, hands-free threading of a calender processing an elastomeric mix as admitted by the prior art (see comments regarding U.S. Pat. No. 4,871,409 above).
Accordingly, a method and apparatus for solving the sticking issue upon start-up in a more reliable and cost-effective way without degrading the material properties of the sheet produced by the calender would be beneficial. Such a method and apparatus that can allow for the automatic and hands-free threading of the apparatus would be particularly beneficial. Additionally, such a method and apparatus that can help maintain uninterrupted and continuous production of the calendering system after startup would also be useful.